1. Field of the Invention
The present invention generally relates to surgical sutures, and more specifically relates to surgical sutures having projecting barbs used for anchoring the sutures in tissue and prosthetic devices.
2. Description of the Related Art
Surgical sutures are used for closing wounds and surgical incisions, and repairing damaged muscles, vessels, and tissue. Typically, a needle is attached to one end of the suture, and the needle is drawn through tissue to form one or more loops holding the tissue together. The suture is subsequently tied off in one or more knots so that the tissue will remain drawn together, or so that a prosthetic device will remain anchored in place.
Although sutures are very effective for closing wounds and incisions, there are a number of problems associated with conventional sutures. Many of these troubles are directly related to the knots used to secure sutures in place. If the knots are not tied properly, defects may arise including slippage, knot breakage, and re-opening of the wound or incision. In addition, using knots to secure sutures may distort tissue, restrict blood flow, increase the formation of scars, impede wound healing, and result in infection.
In response to the deficiencies associated with conventional sutures, barbed sutures have been developed. Unlike conventional sutures, barbed sutures have projecting barbs that allow the suture to be used to close wounds, approximate tissue, tighten tissue, and attach prosthetic devices without using knots. U.S. Pat. No. 5,931,885 discloses a barbed suture that is used for cosmetic procedures such as brow-lifts and face-lifts.
Referring to FIG. 1, a barbed suture 20 is generally formed by cutting a core thread 22 with a cutting blade 24. FIG. 1 illustrates an exemplary cut, whereby the cutting blade 24 first cuts into the core thread 22 at an angle β of approximately 30 degrees relative to a longitudinal axis x-x of the core thread to a depth of approximately 0.08 inches, and subsequently further cuts into the core thread for a distance of approximately 0.024 inches at an angle of approximately 0 degrees to form projecting barbs 26. After the cut is completed, the barb 26 remains connected to the core thread 22 through a base 28. During cutting, the core thread 22 is typically placed and held on a cutting vice or support in a manner well known in the art. A template may be used to guide the cutting blade 24.
Cutting barbs as shown in FIG. 1 requires the use of a mechanical shearing methodology that will rapidly dull the cutting edge of the cutting blade, thereby requiring frequent changes of the cutting blade. The cutting methodology is also negatively affected by the typical extruded diameter variation in the target thread. This variation in diameter requires a cutting head that must be frequently adjusted in fine diameter threads as small changes in thread diameter result in significantly thinner/weaker barbs, or in thicker threads resulting in thicker, stiffer barbs that will cause a variation in frictional drag during application.
The cuts in the core thread act as stress concentration points. In applications where a significant or pulsatile load is placed on the barbed suture, i.e., heart valve repair or replacement procedures and orthopedic applications, a given barb may fail, or begin peeling away from the core thread. Once this occurs, due to the fibrous nature of the suture material, the barb may be stripped off the core thread along a significant length of the suture causing catastrophic failure of the suture.
For example, referring to FIG. 2, after the cutting steps described above, the cut barbs 24 remain flexibly coupled with the core thread 22 via the bases 28. When a leading end 30 of the barbed suture 20 is pulled in the direction D1, the barbs 24 collapse inwardly toward the core thread 22, and deflect toward a trailing end 32 of the barbed suture 20. When the trailing end 32 of the barbed suture is pulled in the direction D2, trailing edges 34 of the barbs 26 push against the surrounding media so as to deflect the barbs outwardly and away from the core thread 22. As the barbed suture is pulled in the direction D2, great stress builds upon the previously cut base sections 28. As a result, one or more of the barbs 26 may fail at the base sections 28 and delaminate from the core thread 22. This type of structural failure may result in catastrophic failure of the barbed suture, and may also result in serious injury to, or the death of, a patient.
In order to improve the reliability and durability of barbed sutures, some have attempted to enhance the strength of the connection between the barbs and the core thread. Unfortunately, these efforts have provided barbed sutures having rigid or relatively inflexible barbs provided along the barb shaft. The rigid barbs remain inflexible when pulled through tissue, impart significant drag, and damage tissue during passage. The drag and tissue damage effects become exaggerated when the barbed elements oppose each other along the barb shaft resulting in sawing of the tissue during motion. Due to this “sawing effect”, the tissue may be damaged.
In some instances, braided barbed sutures having more durable barbs are used. In one embodiment of commonly assigned U.S. Patent Application Publication No. 2007/0005110, the disclosure of which is hereby incorporated by reference herein, a prosthetic heart valve has a valve sewing ring and braided barbed sutures are disposed in the valve sewing ring by first passing the sutures through an annulus and then passing the sutures through the valve sewing ring. Approximately 12-20 sets of braided barbed sutures are passed through the valve sewing ring to secure the prosthetic heart valve in place. The heart valve is then parachuted down the sets of barbed sutures and seated in place within the annulus. After the heart valve has been parachuted down into place, the barbs prevent the valve from being moved in the opposite, upward direction for holding the heart valve in place without requiring knots.
In spite of the above advances, there remains a need for barbed sutures having improved reliability, durability and efficacy. In addition, there remains a need for barbed sutures that are easier to manufacture and deploy. There also remains a need for barbed sutures that cause little or no damage to tissue as the suture is passed through the tissue while retaining their structural integrity.